This proposal seeks continuing support for a program of research to identify DNA markers associated with general cognitive ability ("g"), which is the most highly heritable dimension in the domain of behavior.The strategy of the ongoing study is to genotype children who represent the high and middle (and low) of the normal distribution of "g." The genotyping focuses on DNA markers in or near genes of neurological relevance. Significant allelic associations in the original sample are replicated using an independent sample of even more extreme high and low "g" individuals. The proposed study has three goals: 1) it will focus on the high end of "g;" 2) it will increase statistical power to detect effects by increasing sample size by obtaining a new replication sample of 50 individuals with IQs exceeding 175 from the Study of Mathematically Precocious Youth and a new sample of 50 middle "g" control individuals; and 3) it will extend the study of "g" to specific cognitive abilities by sampling SMPY 50 individuals with high mathematical scores but lower verbal scores and 50 with the reverse pattern of abilities. Allelic associations between DNA markers and high "g" that emerge in the current combined sample of 50 high "g" and 50 middle "g" controls will be replicated in new samples of 50 extremely high "g" individuals and 50 middle "g" controls. Replicated DNA associations will be genotyped for the sample of 50 high verbal individuals and 50 high mathematical individuals. DNA from these permanent cell lines will be made available to other qualified investigators.